Offset preventing material



PatentedMar. I8, 1941 Y I OFFSET PREVENTING MATERIAL Herbert F. Gardner, Chicago, Ill., assignor to Stein, Hall Manufacturing Company, Chicago,

Ill., a corporation of Delaware No Drawing. Application September 22, 1939, Serial N0. 296,075 I 10 Claims. (Cl. 101-416) This invention relates to the prevention of offmechanism. This disadvantage may be overcome set or smutting in printing caused by piling sheets to some extent by continuously agitating the offone upon another after they have been printed. set preventing material in order to keep the starch The invention relates more particularly to new in suspension. Such an expedient is undesirable and improved ofiset preventing materials. y from the practical point of View, however, be- 5 The prevention of offset in printing is a well cause it necessitates the use of additional agitarecognized problem which has caused many tion equipment which would not be necessary difficulties. It is a customary procedure to stack otherwise and which, therefore, adds to the cost the printed sheets on top of each other as they 1 of the process. 1 i

leave the printing machine or press. The back With the foregoing considerations in mind, one

of each sheet is then printdrin a subsequent of the objects of the present invention is to pro- Operation, Inasmuch as the;stacking of the vide a new and improved type of offset preventprinted sheets places the printed side of the sheet ing material containing starch which does not in contact with the back of a succeeding or preu have to be agitated during or immediately before l5 ceding sheet, any smutting of the printingink its application. A feature of the present invenonto the hack of said sheets will necessarily intertion which contributes to the accomplishment fere with or destroy the value of-a succeeding of this object is the provision of an offset preprint It is accordingly highly desirable that this venting material containing a water insoluble smutting or offset, as it is usually called, be starch, for example, raw or ungelatinized starch eliminated. i

Many methods and variout types of materials pending or carrier medium. The latter should have heretofore been proposed foroffset prevenbe of such character that it does not interfere tion. One method involves the temporary inwith spraying or other customary methods of apsertion of so called slip sheets between the conplying liquid offset preventing material and at the secutlve printed sheets. It has also been customsame time it should have sufflcient suspending 25 ary on cylinder printing presses to apply a liquid power to maintain the starch in uniform sus-; ink repellent or inkdrying material to freshly pension.

printed sheets by spraying such materials upon In order to accomplish the objects'of the inthe sheet so as to coat the entire imprint with vention it is essential that the suspending medium the ink repellent. Probably the materials which or carrier for the starch have the property of 30 are most, widely used as spray materials for ofiset drying relatively rapidly so that the offset preprevention are solutions of gum arabic and other venting material may be applied by a suitable similar water soluble materials. Each materials sprayer or spray gun without substantially wetare normally employed in theform of alcoholic ting or spotting the printed sheet. Furthermore,

solutions and the fumes or mists which are formed the carrier medium must be such that it does 35 where they are used are very undesirable. not react with or otherwise affect the ink on the It has also been proposed heretofore to prevent printed sheet. As another requisite for the acthe offsetting of ink from a freshly printed surcomplishment of the objects of this invention, face by applying thereto in 'mist form a mixture the carrier medium should be such that when 40- consisting substantially entirelyof a. liquid and pp d to t Printed Sheet as a P of the a powdered material, at'least the greater poroffset preventing material it is substantially nontion 01 which is insoluble in the liquid, com tacky or non-adhesive and should not cause the starch being mentioned by way of a specific exprinted sheets to stick, together.= Additionally,

. ample. The present invention is concerned with the carrier medium employed in accomplishing the prevention of offset by the use of a starch. the objects of this invention should be such that 45 Among the problems encountered in the use or it can be used in concentrations which will not a liquid material consisting substantially entirely cause masking of the printed matter. of a starch and a liquid is the non-uniformity of In carrying out the invention it has been found application of the ofiset preventing material. that a substantially non-adhesive hydrogel may intimately mixed in'a liquid medium with a sus- 2o Raw or ungelatinized starch tends to settle from beused as the carrier or suspending medium. 50

a suspension. thereoi in water and unless some 1 The term .hydrogel is used herein to define means can be provided to prevent this settling, substances which form colloidal gels with water. the natural resultisthe'applicaflonoothe printed Among such substances are bentonlte, alumina sheets of a non-worm or starch and ,"cream" (such as obtained by dissolving alum in possibly the eventualielogging of the spraying water and slowly adding an alkali) and coagulated as silicic acid. Bentonite is the preferred hydrogel medium. When used in suitable concentrations it has the necessary suspending power'to suspend starchin a liquid offset preventing material and likewise has the other characteristics previously mentioned,

Generally stated, therefore, the invention comprises the preparation of an offset preventing material formed from a liquid medium and a substantially water insoluble amylaceous substance such as raw or ungelatinized starch in an intimate dispersion with a substantially non-adhesive hydrogel suspending medium, preferably a mineral hydrogel. The concentrations of the various materials preferably correspond to certain preferred proportions, as hereinafter more fully described.

In practicing the invention, it has been found that offset preventing materials made from starch and a hydrogel, as herein described, sometimes have a tendency to form a precipitate or deposit on metal containers or in spray equipment, particularly where several different types of metals are employed in such equipment. This is due to the well known fact that colloidal particles carry electric charges and will therefore migrate to one or the other metal of an electro-couple depending upon the positions of the metals in the electromotive series.

Another object of this invention is to provide offset preventing materials of the type described in which the formation of such deposits either does not occur or is substantially retarded. To the accomplishment of this object a feature of this invention involves the addition of an alkali or acid reacting substance to an offset preventing composition formed from starch and a hydrogel of the type described. The acid or alleali reacting substance is added in amount to adjust the pH of the carrier medium, preferably to the isoelectric point of the hydrogel used. At this point the hydrogel carries no electric charge and therefore does not migrate, Although there is a tendency for a hydrogel to precipitate at its isoelectric point, this does not impair its usefulness as a suspending agent when used in the proportions and manner hereinafter described.

As an illustration of the above phenomena, 1 give the following experiments. Two electrodes of iron and tin, respectively. were partly immersed in the following solutions, and the exposed portions of the electrodes were connected by means of a copper wire:

I Parts Bentonite Starch 300 Soda ash 3 Water l 2000 The resulting pH was 9.7. I

II Parts Bentonite 100 Starch 300 Soda ash 7 Walter 2000 The resulting pH was 10.1.

m Pants 'Bentonite 100 Starch 300 Soda ash 10- Warter 2000 The resulting pH was 10.25.

Upon standing for awhile, and mor particularly after standing over night, there is noted a deposit on the iron electrode in experiment I and on the tin electrode in experiment III, but there is no deposit on either electrode in experiment II. t

Any alkali or acid reacting substance is effective for this purpose to a greater or lesser extent, depending upon the particular type of substance used. Among such substances are, for instance, soda ash, magnesium oxide and other al- 11 kaline materials, including as a general class of materials, the salts of weak acids with strong bases, and salts of strong acids with wo k bases. This aspect of the invention is notlimlted, however, to the use of salts because th readily availl: able oxides and hydroxides can also be used if they have an alkaline reaction in an aqueous medium. The alkaline reacting substance chosen would normally be one which under the conditions of use does not react with the starch and 21 has no harmful effect upon the printed material to which the offset preventing composition is to be applied. Thus, as will readily be understood by those skilled in the art, it would be undesirable for the purpose of this invention, to employ an 21 alkaline reacting substance such as sodium hydroxide or potassium hydroxide in any concentrations that would tend to gelatinize the starch. Hence, if such materials are employed at all, they are preferably used in amounts such that their 3 concentration in the offset preventing material is less than about 1% by weight of the liquid.

It is sometimes desirable in the practice of the present invention to incorporate with the oil'set preventing composition other materials that have 3| a known specific action or efiect. Thus, it may be desirable to add to compositions of the character previously described fermentation or souring preventives such as formaldehyde, paraformaldehyde, other formaldehyde derivatives or other substances which are known to have a similar effect. Among the substances which may be added for a similar reason is magnesium oxide, preferably in the form known as light' magnesium oxide." The use of this type of sub- 44 stance has the advantage that it not only prevents any fermentation or any tendency toward fermentation over asubst-antial period of time, but also it is an alkaline reacting substance, and therefore, tends to inhibit or retard the deposi- 5 tion of solids from the offset preventing material onto spray equipment, containers or other metal equipment employed in applying the material. Thus, two functions are accomplished by the use of only'one additional material.

In preparing compositions of the character described it is also sometimes desirable to incorporate therewith a volatile solvent or diluent in sufficient amount to accelerate the drying of the sprayed material. For this purpose it is preferable to use a water-miscible volatile liquid such as ethyl alcohol or any other volatile liquid having similar properties. The particular type of volatile liquid chosen for this purpose is not limited except to the extent that it should be a substance that is substantially unreactive with starch and with the other ingredients of the offset preventing composition and also a substance which has no harmful effect upon the particular type of printing ink which is being used. Ordinarily, of course, this substance will be substantially completely volatililzed and will not tend to condense upon the printed material.

The following examples are given in order to illustrate the types of compositions which may be (I prepared in accordance with this invention but represent preferred embodiments of the invention and are not intended to limit it. In the examples the quantities are stated in parts by weight unless otherwise indicated.

Example I An offset preventing material was made up by Y mixing together the following ingredients:

Parts Bentonite (grit-free) 6 Corn starch 20 Watch-" 200 The mixing was efiected at normal temperatures. It was found that the starch stayed in suspension and this material gave good results as an oiiset preventing material when applied by spraying to printed sheets.

Example I! An offset preventing material was prepared by mixing together the following ingredients:

Bentonite (grit-free) lb 1 Corn starch lbs '3 Water lbs 20 Formaldehyde cc-.. 14

This material also gave excellent results in the prevention of oilset when sprayed onto printed sheets.

Example III Another oilset preventing material made in accordance with the present invention consisted of the following ingredients mixed together at substantially normal temperatures:

Parts Bentonite (grit-frown 100 Corn starch- 100 Soda ash '7 Water- 2000 Formaldehyde 3 This particular type of composition illustrates the use of an alkaline reacting substance, namely, soda ash, to prevent or retard deposition of solids on the'spray apparatus.

Example IV An offset preventing material may be mixed in dry form and sold as such to the printer who may then prepare a liquid dispersion of the material at his convenience merely by mixing the dry form of the material with water. A suitable dry, commay have the following forposition of this type mula:

Star h parts- .200 Bentonite (grit-free) --do 100 Paraiormaldehyde ....percent This dry form of the composition may be mixed with water in the proportions of 2 lbs. of dry mix- Another type of composition which may be pre- 75 pared in accordance with this invention is made of water.

by mixin together at substantially normal temperatures the following ingredients:

, Parts Bentonite (grit-free)- 25 L ht magnesium oxide 10 Corn starch 65 Water 450 This composition is an excellent offset preventing material and tests with magnesium oxide over a substantial period of time have shown that no souring of the composition takes place.

This dry blend may be mixed with water at ordinary temperatures and in proportions of 2 lbs. to 2 a gallon of water to give an ofiset prevention spray material well suited for the prevention of oifset in high speed printing operations;

It will be understood that the invention is subject to certain variations in the manner of its practical application. For instance, it is not limited to the use of any particular type of starch. Grain starches and, more specifically, corn starch. however, are preferred. Other suitable starches which may be mentioned are those derived from wheat, oats, rye, sago and tapioca.

The proportions of the various materials and the concentrations thereof may vary within oertain limits and may be adjusted or modified in order to meet the needs or the type oi. spray equip ment or other means which is to be used in applying the offset preventing material; The amount of hydrogel (e. g. bentonite) should be at least suflicient to maintain or hold the starch in suspension but should not be so great that the viacosity of the oifset preventing material is increased to the point where it cannot be conveniently applied. Ordinarily a concentration of hydrogel (e. g. bentonite) will be within the range of about 1% to about 5% based upon the amount The weight ratio of solids to water should preferably be within the range, of about 1:1 to about 1:15 and the weight ratio of starch to hydrogel (e. g. bentonite) should preierablybe from about 35:1 to about 1:1. Thus, it is possible to make a suitable onset preventing material in accordance with the invention containing say 100 parts of starch to 3 parts of bentonite. Under most circumstances about 3% bentonite based upon the amount of water is suflicient to maintain in suspension for the purpose of this invention a 1 Parts Bentonite (grit-free) 3 Starch 100 Water 170 The tollowing table is given toillustrate oiiset spray solutions made in accordance with this invention haying varying solids contents;

Ben- Addiiion- Solids to Bentonton- Water a1 water Pcrcontwater ite to ito Starch A solids 12:1 starch 3 100 0 2. 9 1:31 I :0 3 100 5 3.8 7.2 1:13 l:l% 3. 1110 7.5 10.8 1:8.3 1:114 3 100 11.5 13.9 1211.2 1:5 3 104) 15. 0 16. 7 1:5 1 111% 3 100 18. 8 19. 1 1:4. 2 1:81; 3 1110 22. 5 21. 2 1:3. 7 1:10 3 100 26.5 23.1 1:3.3 l:ll% 3 100 30.1) 24. 0 1:37 0 1: 13% 3 100 34.0 26.4 1:28 1:15 3 100 37. 5 27.8 1:2. 6 1:1635

A=wator necessary to wet starch.

In the above table it will be observed that the amount of water necessary to wet the starch is given as approximately 75%, although it will be understood that this amount of water may vary somewhat depending upon thetype of starch. The quantities given in the first four columns of the table are in parts by weight. The percentage figures in column 5 are also based on total weight of the composition and the ratios given in columns 6 and 7 are weight ratios.

In any of the aforesaid compositions a volatile substance, for example, ethyl alcohol, may be added in order to accelerate the evaporation of moisture when the composition is applied. Normally up to 25% of ethyl'al'cohol may be used in the oiTset preventing composition based upon the weight of the composition.

It is contemplated that the compositions prepared in accordance with this invention are to be applied by spraying, although it will be understood that other methods of application may be employed. A feature of the invention, however, resides in the fact that these compositions are eminently suitable for spray application to printed materials. Among the spraying methods which may be employed arethose described in Buoy, U. S. Patent No. 2,078,790, Paasche, U. S. 2,110,052. Green et al., U. S. 2,110,218 and 2,110,219, and Paasche, U. S. 2,114,723. The invention may be used in connection with all types of printed matters either in black and white or in color.

The method of application to successive printed sheets should preferably be such that the oflget preventing material is applied to the atmosphere in the vicinity of the printed portion of the printed material and is substantially dry by the. time it reaches the printed sheet. This is'po8- sibie when using the offset preventing materials of the present invention even though the printing operation is being conducted at a, very fast rate, say, 3200 sheets of size 3' x 5' per hour. The ingredients of the composition, moreover. do not tend to react with or otherwise affect all ordinary types of printing inks or colors including those inks containing cellulose derivatives and cellulose derivative solvents.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. An oilset preventive comprising a substantially water insoluble amylaceous substance and a substantially non-adhesive hydrogel suspending medium 'for said substance, the weight'ratio of said water insoluble amylaceous substance to said hydrogel suspending medium being .within the range from about 35: 1 toabout 1: 1.

2. An offset preventive comprising a substanti'ally water insoluble amylaceous substance, a substantially non-adhesive mineral hydrogel sus pending medium for said amylaceous substance, and an inhibitor of such character and in such amount as to substantially reduce the electric charge 01' the hydrogel and thereby retard the deposition of the solids content of said composition on metallic surfaces but of insufiiclent concentration to gelatinize the amylaceous substance, the amount of said inhibitor being sufflci'ent to adjust the pH of the hydrogel to apprommately its iso-electric point.

3. An oiiset preventive comprising a substantially water insoluble amylaceous substance and bentonite intimately dispersed in water in proportions of about 1% to about 5% bentonite based on the amount of water, a'solids to water ratio within the range of about 1:1 to about 1:15 and a ratio of said insoluble amylaceous substance to bentonite from about 35:1 to about 1:1.

i. A dry base material adapted to form an oil'- ing medium being within the range from about 35:1 to about 1:1.

5. The method of preventing offset from a freshly printed surface which comprises applying in finely divided condition in the vicinity of such surface an oifset preventive comprising a water insoluble amylaceous substance and a substantially non-adhesive hydrogel suspending medium for said substance, the weight ratio '01 said water insoluble amylaceous substance to said hydrogel suspending medium being within the range from about 35:1 to about 1:1.

6. The method of preventing offset from a freshly printed surface which comprises applying in spray form to the vicinity of such surface an aqueous liquid containing a water insoluble amylaceous substance suspended in said liquid with a substantially non-adhesive mineral hydrogel suspending means, the weight ratio of said water insoluble amylaceous substance to said hydrogel suspending medium being within the range from about 35:1 to about 1:1.

7. The method of. preventing oflset from a freshly printed surface which consists in applying to said surface an offset preventive comprising a. water insoluble amylaceous substance and bentonite intimately dispersed in water in proportions of about 1% to about. 5% bentonite based on the amount of water, a solids to water ratio within the range of about 1:1 to about 1:15, and a ratio of starch to bentonite from about 35:1 to about 1:1.

8. The method of preventing offset from a freshly printed surface which consists in applying to said surface an offset preventive comprising a'water insoluble amylaceous substance and bentonite intimately dispersed in water in proportions of about 1% to about 5% bentonite based on the amount of water, a solids to water moomo ratio within the: range of obout; 1:1 to mono 111%,, onoEL o room oil storm to oomzomto from moot so: 1 to ohout 1:1, sold oifoo'; preventive oiloo eon homing on ollmlme mootmo ouoofi'oooo in mm ciaoma omouot to adjust tho pH of tho hontomto to omprommmely its loo-elootrio point.

9. An offset preventive comprising o summontiolw Wotan" imsoliuolo omyloceouo oomtonoo omd o substantially non omxoowe hydroge ouopond m medium for said suootooco mtimotoly om parsed in WZEZtE-ZK m proportions of mom; 1% to about 5% of'hydrogol hosed on tho omoom of Woman", o solids w Wotor mono withm mo oozm'o oi about 1:1 to mom 1:15 moo o Weight mtfio ofi' mom 0mm oloooouo oohotoooo to ookoa Rag doom;

from about 352R to out 1121..

11m. Anoflsefi: orovonwvo oomomlomw o Watson" m soluble amyloooowo oobotoo moot oomomm in timotely dlsmon' m o otoo m mroooofiafiomo of about 1% to about 5% loomomfso mood on tho amount of water, o oolmo to WMGEBR Womhfi; mom Within the mnoo of ooomt 1:1 to oooofl; Ezflfi ammo] o mom of omyloooouo ouoommo to oomomoo from ooout 35:1 to about 1:1, ooid ooot provoooflvo moo oonmmmo an olhmolmo roootiooz oohotoooo to. Wolf fioioot amount to mom; tho pH of tho bomiooioo to ooproximatow ito ioo-olooimo point 1 u is, F. HARM 9. 

